I'll give you +1 if you clean off all that grime and take a picture that lets us see the details... =)
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darkcanuckApr 6 '11 at 14:19

1

And once upon a time you could buy (cheap) clamps at bike shops specifically designed to do this. I used a set on my first touring bike.
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darkcanuckApr 6 '11 at 14:20

I know for a fact that hose clamps are available in Canada.
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DC_CARRApr 6 '11 at 16:29

@darkcanuck - That'd be tough, since the bike is in a landfill now. But this picture is slightly clearer, and if you click through to my picture, I've added notes to show where the hose clamps are.
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Neil FeinApr 7 '11 at 4:20

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Just going to say, when buying the hose clamps, make sure you can fully unscrew them if you're planning to put them on the inside frame. Nothing worse than getting some, going home, and finding out they're designed so they can't open up and won't go on.
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SlokunApr 8 '11 at 18:03

I've been facing the same issue, trying to mount an additional bottle cage to the underside of the downtube on my mountain bike. I haven't settled on one particular solution yet, but I found this site helpful as it outlines various different solutions: http://www.nordicgroup.us/cageboss/